From: jj4public@nospicedham.vfemail.net   
      
   On Sat, 21 Jul 2018 02:56:31 -0400, Rod Pemberton wrote:   
   >   
   > FYI, IIRC, the 0xCF9 port method is specific to certain motherboard chip   
   > sets, but I don't recall which.   
      
   Oh, OK.   
      
   >> Since these two still require BIOS, how did the BIOS actually reboot   
   >> the system? Cold boot, that is.   
   >   
   > Setting or clearing the reentry address is just a precaution, since   
   > warm and cold booting is controlled by two values: CMOS shutdown byte   
   > and BDA POST reset flag.  I.e., if you mismatch them incorrectly, you   
   > could vector.   
      
   But how did BIOS do it? I don't want to execute any code on the BIOS area,   
   so no interrupt call, and no code jump to Fxxx:xxxx. i.e. I need to perform   
   the reboot from my own code.   
      
   Also, is the CMOS shutdown register works alone? Or does it still require   
   BIOS code? Because I've already tried putting all values into CMOS register   
   0Fh, and the system still won't reboot when tested under VirtualBox. It   
   wasn't run under any OS, and the system is running on real mode (it's during   
   a disk bootstrap). The system is not an U/EFI system.   
      
   The code I use is:   
      
     mov al, 8fh   
     out 70h, al   
     mov al, 0   
     out 71h, al   
      
   The code to test all values is:   
      
     mov cx, 100h   
   @doit:   
     mov al, 8fh   
     out 70h, al   
     mov ax, cx   
     dec ax   
     out 71h, al   
     loop @doit   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)